texts: Could the universe have evolved differently?

texts: Given the initial conditions at the Big Bang, could our universe have evolved any differently? In other words, did the initial conditions predetermine every stage in the evolution of the universe to this day, or - if we "roll the tape backward" and play it again - could the universe be entirely different on the macro scale (eg. no stars and galaxies)?


texts:
What existed before the big bang?

What all thing are there inside big bang object ?.


texts: What could be observed with LOFAR in 230 MHz - 10.0 MHz wavelength?

texts:
Nuclear astrophysics greatly interests me and i was wondering if there is something that could be observed with the LOFAR project in this wavelength that would benefit the field?

Also some general information about this wavelength in astronomy or pointers to information sources would be greatly appreciated.


texts: What is the temperature 55 km beneath the surface of Mars?

texts: What is the temperature 55 km (34.18 miles) beneath the surface of Mars?  The reason I ask is that I want to know if it might be habitable for a possible future colony if they could dig that deep (which might be easier in the lower gravity environment).  If the answer to my previous question is correct, this is the depth that the atmospheric pressure would be equivalent to that on Earth. At what depth on Mars would the atmosphere have equal pressure of that on Earth?


texts: In what form was the space at singularity?

texts:
It is somewhat imaginable for all the matter or energy to be condensed in sub-atomic size. But what about space? The space is neither 'matter' nor 'Energy'.

If there were no space at singularity where did it come from?


texts: Second Telescope: Maksutov Cassegrain vs Refractor

texts:
I bought my first telescope, a 3-inch refractor a few weeks ago. It has been a wonderful experience seeing the Moon, Jupiter, Saturn magnified and Andromeda, M33, M81 and much more for the first time.

Now I wish to get my second telescope. I was considering :
Explore Scientific ED APO 102mm F/7
Bresser Maksutov Cassegrain 152mm F/12.5

I live in a high altitude region with Bortle 3 skies. I hope to see basic details on Jupiter, Saturn and Mars at high contrast and clarity and perhaps the disc of Neptune. Also occasionally deep sky objects. Portability and fast setup time are also a consideration. The MC is about 60% of the price of the APO.

In addition to my 26 & 12 mm Plossl eyepieces I plan on getting a 50mm Erfle (Field Stop 40mm) and a 6mm Plossl.

For mount, I was contemplating between Bresser Exos 2 and iOptron CEM25P.

I wish to know your experience with refractors and MCs, in general, or with these specific models. Since the MC is cheaper and has a bigger aperture, will the APO have any advantages eg.contrast? Also, what are your thoughts on the mounts?

Thank you for your answer!


texts: How to I calcuate observed position of the Sun and Moon using the SOFA C library?

texts:
There are a number of answers on here that skirt the topic, but no concrete answers.
I currently have an implementation based on "Astronomical Algorithms by Jean Meeus" for stars, moon, and sun written ~2007. The stellar positioning is not accurate enough for my upcoming application so I switched that over to the SOFA library (very easy and straight-forward). Just take catalog data drop it into a magic function and BOOM you have RA and Dec.
I am currently attempting to replace the rest of the Meeus algorithms with the SOFA library and am finding my knowledge lacking and the size of the SOFA library overwhelming.
From what I have found, the epv00 heliocentric coords can be reversed somehow to get geocentric coords of the Sun. How would that be done and is that GCRS? Which I can then use for the standard GCRS->observed chain from the cookbook? If that is not GCRS, can I make it GCRS? Should I?


texts: It is possible to combine a reflector and a refractor telescope together?

texts:
I know it sounds crazy, but is it possible to
connect a reflector telescope and a refractor telescopes (like monocular for bird watching) together to build a better telescope?


texts: Why can there be several seconds of lag between a binary neutron star merger and the emission of gamma rays from the same area?

texts:
Answers to: Gravitational waves and gamma ray burst: how were the error bars determined for this speed of gravity calculation? Was $H_0$ used? go into substantial detail explaining this determination. These have been helpful, which encouraged me to try to read the linked paper again. However, based on comments and the paper itself, I see that assigning limits to what sounds to me to be an emission lag of several seconds between the end of the merger and a subsequent gamma ray emission from the same general object/area had to be at least considered and included in some way.
Here I'd like to ask only about this lag. While I'd also like to know what produces the time-lagged gamma ray emission I'm not sure a priori if that is a different question and/or if it's been answered already.
Question: Why can there be several seconds of lag between a binary neutron star merger and the emission of gamma rays from the same region?


texts: Can Pluto be seen with the naked eye from Neptune when Pluto and Neptune are closest?

texts: When Neptune and Pluto are closest, about 100 million mi (160 million km) from each other, would an observer on Neptune (or rather on one of its moons, since Neptune is gaseous) be able to see Pluto, and maybe even Charon, with the naked eye? If not, could Pluto be seen in average binoculars? I think Pluto would appear a bit smaller than Mercury from Earth (but at much lower apparent brightness because of the distance from the Sun).


texts: Ptolemy’s understanding of the planet’s whereabouts

texts:
I imagine that Ptolemy’s epicycles were performed as real circles - around equants - in two dimensions, e.g that he was able not only to give the angles to planets and the Sun as seen from the Earth, but actually able to point out the location in space in a projection in two dimensions or otherwise, of all then known planets in the system.
He would then have had the same type of knowledge as Kepler had, at least in principle, albeit with lower accuracy.
Is that actually the case?


texts: Very near GAIA DR2 sources - has Proxima Centauri been dethroned?

texts:
I made an extract of GAIA DR2 data for parallaxes greater than 500mas. Surprisingly I see a very significant number of sources with parallax greater that 1000, making them much closer than Proxima. This should lead to excited newspaper headlines, but i haven't seen those yet... Am I missing something?

You can see my extract of data here:

https://gist.github.com/agnes1/1492e94b5e9c0ef71f6ae7944964b666

Some GAIA source_id rows to look at include:

4039503676370417664

4042946384760661504

4042338732771057920

4046453826887613696

But there are many more. The closest source I find is 4062964299525805952 with  parallax of 1851mas. It has a phot_g_mean_mag of 19.63355... Would I be right in assuming this is a brown dwarf?

Another thing I note is that there is a surge of vmag 19/20 sources within 10 parsecs. These are obviously so faint GAIA doe not detect similar sources beyond 10 parsecs. To give some numbers I count 1722 sources (most mag 19/20) within 10 parsecs and only 606 sources in a shell of equal volume beyond that. Again, would these all be (a very large number of) brown dwarfs?


texts: Can someone help me to identify this section of the night sky?

texts: I have this image from a treasure hunt, I'm fairily certain it's a real piece of the sky, but I've been unable to identify it, can anyone help?


texts: What is assembly bias in context of cosmology?

texts: I see the term "assembly bias" being used quite a bit in cosmology literature? I have not been able to find a good primer on what it means, and why it is important.


texts: What other galaxies can be seen with the naked eye in the night sky? Can we see any other galaxy besides Andromeda and Magellanic Clouds?


texts: What percentage of galaxies rotate with trailing arms?

texts:
I am looking for the percentage of galaxies that rotate with trailing arms. I know that only a small percentage of galaxies rotate with leading arms and would like to know whether there are any results that determine the percentage of spiral galaxies that rotate with tailing arms.

I am interested in publications in this topic.

Note:
So far I have found the following:

Land et. al (2008): "Determining the rotation
direction in this way is accurate for 96% of galaxies
(Pasha & Smirnov 1982)"
Pasha & Smirnov (1982)
Buta et al. (2003)

Do you know of any newer publication on this question? More recent than Pasha & Smirnov (1982) where the sample is quite small?


texts: Why can't light escape from a black hole?

texts: I've heard that light can't escape from a black hole. Can it? If not, why?


texts:
The latest information suggests that Earth's water came from Meteorites . The Moon was also bombarded by Meteorites and yet it has no water. Is this because it lacks an atmosphere and its water was lost in space ?

On further thought on this matter, it occurred to me that Mars has an atmosphere and yet it has no oceans either, just like the Moon . So Mars I assume was bombarded by meteorites, just like the Earth was and it has a stronger gravity than the Moon, yet it doesn't have oceans either ? So what happened ?


texts: How does gravity affect a physical clock?

texts:
In all the explanations for time dilation and how gravity affects time a common example which is used is "Clock near to the ground will tick away faster than clock away from the ground due to gravity".
But what exactly does this mean ? How does a regular clock gets affected by gravity, does the second hand slows down ?
If it has to do something with gravity affecting the inner working of wind up and pendulum clock will this also affect digital clock ?

** I realize I am missing the fundamentals of lotta things in this question, apologies for the stupid question in advance **


texts:
Auroras on Earth are caused by interactions between the solar wind and the magnetosphere. I've also seen a few pictures of auroras on Jupiter and Saturn.
Mercury has a global magnetic field. Does it also have auroras? If so, what do they look like?


texts: What is the density of stars in our region of the galaxy, up to say, 1000 light years distant?

texts:
If we imagine a sphere of radius one light-year centered on Earth, it contains only one star - our Sun.

If we imagine a sphere of radius ten light-years centered on Earth, it contains about 10 stars, according to this wikipedia page.

If we imagine a sphere of radius one hundred light-years centered on Earth, about how many stars would it contain?

If we imagine a sphere of radius one thousand light-years centered on Earth, about how many stars would it contain?


texts: How do I understand a brown dwarf with a M-type spectrum?

texts:
There are a large fraction of M dwarfs which are claimed to be brown dwarfs.

Why do we still use M-type and not create a new stellar type like L, T and Y? The main signature of M is TiO absorption bands. They appear in M-type brown dwarfs?

Is a spectrum enough to judge whether a celestial object is a brown dwarf or not? Or do we need to know its mass?

The earliest type is M3.5. It means M-type objects older than M3.5 are necessarily brown dwarfs? Or is there a safe value, say, M9, is necessarily a brown dwarf? A brown dwarf is necessarily colder than a red dwarf?

There should be more brown dwarfs or red dwarfs?

The reason we do not need to create a new stellar type is the spectra of brown dwarfs are more like red dwarf's spectra?


texts: Obtaining stars vector position in relation to the center of the galaxy at a given date

texts:
How can someone obtain such vector, for stars in the Milky Way?

Input should be star data (from a catalog, eg: Hipparcos) and Julian Date.

Output should be a Vector Position (in pc) in relation to the galactic center.


texts:
I remember a few years ago hearing that Jupiter was an anomaly in the landscape of exoplanets. Back then, most Jupiter-mass planets discovered were Hot Jupiters, orbiting very close to their host star.

In the last few years since I heard this, many new exoplanets have been discovered. Do we know now if there are many more Hot Jupiters and our own Jupiter is a rather rare occurrence, or if this was an observational bias and there are many more "Cold Jupiters"?


texts: What time and where on earth is the latest solar noon?

texts: For context: I am visiting Portugal from Australia and after observing that people tend to start their days later, I realised that solar noon also seems to occur at a later time - about 1.20pm at the moment. I don't recall solar noon every occurring at such a late time in Australia. When and where is the latest solar noon on earth?


texts: Is it possible for any of the planets in the TRAPPIST-1 system to have moons?

texts: All of the planets in the TRAPPIST-1 system are all orbiting very closely and are somewhat large. Would it be possible for at least one of the planets to have a stable moon in orbit around it? Or would the gravitational interactions between the seven planets and the TRAPPIST system's star make it too unstable for any moons? Would it be possible for any planets orbiting red dwarfs closely to have moons?


texts:
Stacking by Sequator 100 dng photos of night sky taken with a smartphone resulted in a (beautiful, I would say) populated star field where undesired arc streaks are seen all over the field. It is like as the program treated the vast majority of stars as wanted, while (perhaps the less brighter) others are just rendered as they moved along the 100 frames period.
Align stars was chosen then accumulation.
Question: Is this a common problem using Sequator, or at least happened to some of you? Is there any trivial setting or way to redo the stacking? Thanks.
Attached is a compressed copy of the final photo.

the above is cross posted in Photography SE
https://photo.stackexchange.com/questions/124748/arcs-in-stacked-star-field


texts: What is the star whose western traditional name is the longest?

texts:
My definition of traditional name is that name that appears in the stellar catalogs made in classical antiquity by Greeks and Romans and which were later translated and compiled by the Arabs to be later used again by Europeans from the Renaissance. I do not look for traditional Chinese or Mayan names, for example.

Most stars visible without a telescope were given names in Antiquity. These Greek or Babylonian names were transmitted and modified during the Middle Ages by Arabian compilers and many of them are still popular, such as Sirius or Vega.

Other names are longer and more "exotic", like Betelgeuse. I am thinking, for example, of really long and exotic names like Zubenelgenubi (Alpha Librae) or Zubeneschamali (β Librae). Are there any stars whose "ancient" or "medieval" name are longer?

Here is a list of arabian star names, later modified by europeans, but it may be incomplete, because greek catalogues included about 1.000 stars and this list only includes 200.


texts:
I was given a StarNavigator 90 (DS-2090) with a motorized mount (Single-arm, motorized Alt-Az) which works with 8 AA batteries. Only issue is that it eats the batteries so I was wondering what kind of batteries are recommended for motorized mounts?

Also, can I use a 12v battery (such as those gel batteries, or even car battery) to power the mount?

Thank you,
Matias.


texts: The physical processes of emission lines in cosmic nebula

texts:
I think I understand how absorption lines in cosmic bodies occur. But after reading about the emission lines in quasars I am wondering more and more about the physical processes causing the emission lines in cosmic nebula. I hope you can explain these processes to me, more precisely from where to where energy needs to transition and if there are temperature requirements on the involved objects. Below are some of the statements that I encountered and I don't understand:

Emission clouds/nebula need to be ionized - But they need to be only partially ionized, right? If they are fully ionized energy transitions of the electrons wouldn't be possible, so emission lines wouldn't be possible either and there would be only scattering.

Only hot gases create emission lines - Is this really true? Wouldn't it be possible, that a cosmic cloud much cooler than the object illuminating it would also cause emission lines (see drawing below)?

Regarding emission lines from stars I read that they occur due to recombination - is this true? But why only discrete initial energy of the electrons would allow them to recombine with a (partially) ionized atom?

So can you explain the physical processes of nebula emission lines in a bit more detail than the links do? Tnx


texts: Can the moon's gravity influence be observed on the space station's orbit?

texts: In browsing through Astronomy Stack Exchange, I came across this question about orbiting the moon (Is it possible to achieve a stable "lunarstationary" orbit around the moon?).  In further looking, I came across (Can I measure the moon's gravity?) which seems to indicate that with sensitive enough equipment, the moon's gravitational pull could be measured on earth.  This prompted me to wonder if the moon's gravitational pull can be observed on the Space Station's or geosynchronous satellite's orbital path?  And if so, if any compensation (either short-term or long-term) needs to be performed due to the moon's gravity.  I would think it to be relatively inconsequential, but am not sure, hence the question.


texts:
This is Question 17 from USAAAO Practice Round 2015. The answer is D. It would be best if someone can detail out the workings.

  In a nearby star system, two stars are seen to orbit each other every
  8 years. At their closest, the stars are 2” apart. At their furthest,
  they are 18” apart. If a parallax of 0.5” is observed for the star
  system, what is its combined mass in solar masses? Assume an
  inclination of 90 degrees.

  a. 0.5
  b. 1
  c. 2
  d. 4
  e. 8

What I got so far:

Distance to system: 2pc (6.171e16 m)
Minimum separation: 5.98e11 m
Maximum separation: 5.38e12 m
Relative semimajor axis: 2.99e12 m (20AU)
Combined mass: 125 solar masses


texts: What is the shape (along the plane, not up-down) of stellar orbits in flat spiral galaxies

texts:
What I mean is, with a central mass orbits are relatively simple, but orbits around the galaxy are different, in essence as the star orbits through the dark matter halo, the further it moves away from the center of the galaxy the greater the gravitational field, so while orbits tend to slow down as kinetic energy is turned into potential energy, stars are effectively orbiting around more mass the further they are from the center of the galaxy, which might speed them up. The equal areas over equal time rule would seem to no longer apply.

So, ignoring up and down motion relative to the plane of the galaxy, is there a common shape for galactic orbits? Is there a formula? I think eccentricity would still apply, but I don't think the orbits would be ellipses, so it would be a different kind of eccentricity. Would these orbits tend to circularize (in an ideal dark matter cloud, ignoring perturbations. Obviously perturbations would lead to, in a practical sense, unpredictable orbits, not neat and tidy formulas. I gather from a show I caught on the science channel that the Milky Way's magnetic field also plays a role in forming its spiral arms, but I'm asking in an ideal, mathematical sense, what shape would orbits be through a galaxy, from a 2D point of view, ignoring up and down motion.

Update

It occurred to me that the question might be more simply asked by a black hole in effect "orbiting" through a planet or even a low-velocity neutrino (if there are any low-velocity neutrinos). The inside a planet orbit is quite different than the Kepler orbit, because gravity increases as the object moves further away from the center. The overall orbit might still be somewhat like an ellipse but the laws for such an orbit would be different, you would see the highest acceleration at the furthest points from the center though you'd probably still see the highest velocity at the closest point to the center.

Anyway, I'm mostly just curious if those shape has been worked out and what it looks like.


texts:
A Nebula boasts of Too Bright Awesome Colors that includes red, blue, green, orange, white, etc?

They're result of excitation of electrons.

Is there a clear explanation as in which Color is attributed to an atom for Color properties in Cosmos!?


texts: What is the mass and momentum of a relativistic jet?

texts: Relativistic jets from accreting black holes are powerful radiation sources, but carries some ionized matter along. What are the estimates or observations of the mass or momentum flow in such jets?


texts: What does the orbit of multiple star systems look like?

texts:
How can I find simulations of trinary, 4-nary.. etc. star systems?

What do they look like?

For example the Alpha Centauri system has 3 stars and possible planets. What does that orbit look like?

I cannot find any simulation on here, it includes 2 Centauri A and B does not include the third dwarf star Proxima.

We have been observing the system for many years, I would think a lot of simulations would come out of each new star system we find, or are they all very similar to one another.


texts: Will we see gravitational waves from the big bang?

texts:
This is almost identical to an unanswered question already asked, but I want to put it a different way. The announced LIGO event was from a localized source. I assume that gravitational waves from the Big Bang would come from "everywhere" like the CMB, so I don't see how LIGO or the next generation observatory (ie. eLISA) would detect this.

One thing else I would like to know, if anyone is aware: I watched an hour long webcast on You Tube and the question I had during the whole time was asked just as the webcast went "off the air". My question is that, since this announcement is about five months after the detection and since it happened "right away", has anything else been detected over the last five months? (Has LIGO been continuously observing? I know that the upgrade is still in progress and sensitivity should get about three times better.)


texts: What exactly was the Moon's "Evection Resonance"?

texts:
Ward et. al define the evection resonance of the Moon with the Earth and Sun as:

occurring when the lunar perigee precession period equals one year.

Does this simply mean that the angle formed by the Sun-Earth-Moon when the Moon was at perigee was the same every month?
I tried looking at the wikipedia definition of Evection but just found it more confusing.
If it helps, I am curious about the lunar evection resonance because it is often cited as a mechanism to explain Moon/Earth angular momentum shedding necessary if one assumes the Giant Impact Hypothesis of Moon formation.  See Ward and Canup:

The resonance can exchange angular momentum between the Earth-Moon
system and the Earth's orbit.


texts:
Since the surface of Mars is covered with lots of iron and became red because of rustiness of iron,

Source from: live.mrf.io

if we do have plan to live there, can we get tetanus on those rusty thing? I don't know much if we can be immunize to this thing but still it might be lethal at some point if they have tetanus, even a slight stumble might be dangerous.

Update: About being off-topic. I thought posting it in Astronomy would be better because they know much and literally know much more about Mars and its atmos, temp, minerals or something, instead of posting it in Medical-related stackexchange. I mean, it's Mars, Astronomy stuffs knows better, isn't it?


texts:
I know of two methods for finding exoplanets: the transit method and the radial velocity method. These two methods work as follows:

Transit: we observe stars and watch for when a planet obstructs the light from the star.
Radial Velocity: detecting the planet by observing the motion of the star and using Kepler's law.

Are these methods also used for discovering black-holes? What are the pros and cons of these methods, I think that the con of transit is that it's difficult to see the black hole. A pro is that it doesn't matter how many stars there are around the black hole.

With the Radial Velocity method, a pro is that it's easy to detect but requires exactly one companion star (I used this source).


texts: What is the mass of hotspots in the Cosmic Microwave Background radiation?

texts:
A lot of pop science articles (for example, this Space.com article) discuss the cold spots on the WMAP data of Cosmic Microwave Background (CMB) radiation, but have any studies been done on the large mass of hot spots on the right of the image below?

Is this a side-effect of our observation methods or does it represent some actual feature of the early history of the Universe?


texts:
So, I have been trying to figure out the bolometric luminosity of the comet C/2020 F3 (Neowise) on the 22nd of June, 2020. At that time, Neowise was $1.4$ AU away from Earth and had an apparent magnitude of $m=3$. By using the formula $$m=-2.5log\Bigl(\frac{F}{F_O}\Bigl)$$ and $$F=\frac{L}{4\pi D^2}$$ where $F_0$ is the flux of Vega, $F$ is the flux of the comet, $D$ is the distance from Earth to the comet. I found that the bolometric luminosity, $L$ ,of the comet Neowise was around $7.45\cdot10^{14}$ watts when it was $1.4$ AU away from Earth. However, on the 22nd of June, Neowise was also $0.4$ AU away from the Sun. I have tried to use the flux from the Sun at this distance to determine the luminosity of Neowise again. I have found the flux from the Sun at that distance to be $8488.26$ $Wm^{-2}$ using the above formula for flux, but now using $D=0.4 AU$. After that I thought of calculating the luminosity by using flux from the sun times the area of Neowise. Assuming the nucleus of Neowise has a diameter of $5 km$, and assuming that the comet is fully illuminated,
should I assume that the nucleus of Neowise is spherical or circular? And why should the 2 luminosities be different?


texts: Is the Earth losing or gaining distance from the sun overall? Could asteroids over time add weight to the Earth and push it farther from the sun more than having a degrading orbit around the sun? Does asteroids and space dust increase the mass the the outer planets over sustaining or pulling the Earth from the Sun?


texts: When would Oumuamua have entered the solar system?

texts:
So from what I've read, Oumuamua travels at around 26km/s when in interstellar space.

I also remember reading a while back that Voyager was travelling at around 18km/s when leaving the solar system.

Seeing as Voyager took around 35 years (I think) to exit the solar system, I'd guess that Oumuamua entered our solar system around 20–25 years or so ago?


texts: Which force makes planets to continuously revolve around their parent star?

texts: We know that planets revolve around their parent star (or specifically Barycenter), they maintain a specific speed of revolution so that they don't end up smashing into their planet star. Which force or energy do that, so that they maintain their speed? If we have infinite amount of time, would planets smash into their parent star ?


texts: Is it possible to achieve a stable "lunarstationary" orbit around the moon?

texts:
Is there a stable geostationary orbit around the moon?

My feeling is, that the orbit would collide with earth, because of the moon's slow rotation.


texts: Why are we so quick to proclaim the geological inhospitability of other planets based on extremely minimal information?

texts:
Now, I'm not questioning claims that any planet in the Solar System is atmospherically or externally inhospitable, but claims made that other planets have geology that is extremely hostile to colonization (or even, in the case of Venus, further exploration).
Some of these claims are:

Mars's core is frozen.
Mars has no recent volcanic activity.
There are no large deposits of carbonates or other carbonaceous minerals/materials on Mars.
The total quantity of water on Mars is less than 1% that on Earth.
A perchlorate layer covers the entire Martian surface.
The soil of the Moon, Mars, and Venus would need to be massively modified to support plant life.
Venus was volcanically resurfaced in its entirety.
There are never any breaks in Venus's cloud layer, no matter how small or infrequent.

Judgements like this seem very premature given our lack of hard data, especially that of direct measurements of rock strata. For instance, about the first claim, only one functional siesmometer has been sent to the surface, which has only been there for a year and lacks any impact tests, and the only instrument sent to measure internal heat has so far malfunctioned. The 2nd and 7th claims are almost exclusively based on crater counts, which can give tremendously different age values depending on the expected impact rate. The 3rd is based exclusively on remote sensing methods unable to identify underlying strata, the 5th is based on a handful of landings, and the 6th has been called into question by research old and new. For the 8th, no modern space mission has even carried the instrumentation required to confirm this (that is, a high-resolution visible-light camera). All of these seem only possible to confirm or deny with much more extensive exploration, especially on and under the ground.

So, then, what am I missing, if anything? Why is it acceptable to make judgements like these off the information we have? I mean, imagine if a textbook of Earth's geology was writen solely on the observations of a handful of satellites as well as 9 pseudo-randomly-dispersed geologists allowed only a couple tens of kilograms of shallowly-penetrating tools and analysis devices (some defective) each, of which 5 of them are buried up to their knees in rock.


texts: Can impact craters on the moon act like giant radio telescopes?

texts:
Could large craters on the moon be used as reflective lenses for radio signals?

Acting like a large radio telescope reflecting radio waves to a satellite positioned over the crater.


texts: Temperature of a substellar point on an airless tidally-locked planet

texts:
If a hypothetical blackbody planet's components were solid at all temperatures, would the substellar point on the airless tidally-locked (1:1) planet eventually heat up to the surface temperature of the star it is orbiting? This material would be a very poor heat conductor.

Also, would the temperature on the opposite point approach the cosmic background temperature 2.7 K?


texts: Has the sun become way brighter the last years?

texts:
Up to last year, I never got blinded by the sun in everyday situations (e.g. running towards it), at no time of the year I was. But since last christmas, it occured to me more often that I cannot watch in the direction where the sun is because it is so bright that it really hurts me.
My mother and my roommate have observed the same phenomenon independently of me.

This, of course, is only anectodal evidence, which is practically worthless. We all get older and we may have the same kind of "photophobia", or we just forgot about being blinded the last few years and just now consciously felt an remembered it.

Therefore I want to ask this question: is there any objectively observable increase of brightness over the last few months and if so, why?


texts: Can we only see the past of the universe?

texts:
So I was reading some interesting stuff about universe and Big Bang and wanted to make sure one thing. As far as I understand everything we can see about universe is the past, right?

I mean all the galaxies and known stars are many light years away so we have no way to knowing if they still exist, so pretty much we don't know anything about present state of the universe, galaxies and stars. Am I right?

That said, all of the facts are said in present tense like "There are billions of galaxies" or "there are black holes", but in fact, they WERE, because we don't know if they exist now.


texts: Could pure iron from a star make it to Earth?

texts:
Since iron is a stars waste could a star that goes Super nova eject pure iron to travel across the galaxy?

https://space.stackexchange.com/questions/35101/99-99-pure-iron-meteorite


texts: Do we know if the moon had an initial rotation or did it coalesce tidally locked. If it had an initial rotation how long would it take to become tidally locked?


texts: Does Dark Matter affect the motion of the Solar System?

texts: Would dark matter have a similar effect on the Solar System as it does on the Milky Way? I'd imagine it could help hold together some of the Solar System bodies or at least affect their motion, right? Maybe to a lesser extent, but would it be significant?


texts: In what ways can force be applied to a black hole

texts: Besides gravity I have never heard of another force pushing or pulling a black hole. Does an object falling into a black hole push the black hole when it crosses the event horizon? What happens to the kinetic energy of an object that enters a black hole?


texts: How to find out if a galaxy is in a specific cluster

texts: I am trying to find out how to find out if a certain galaxy is located inside a cluster. For the famous ones this is quite easy (sometimes even on wikipedia!), but I haven't been able to do it for some less-known galaxies. I have tried to look them up on Simbad, but I couldn't find it written down anywhere (even for the ones I know to be in clusters). Also generic "googling" has not helped me. Do you have any suggestions?


texts: How to calculate the movement of the object passing near other object in space?

texts:
Assume object A is moving through the space and is passing near the other object (B). Assume the gravitational influence of other objects can be ignored. How to find the equation describing the movement of the object B?

There are 2 cases, object A is moving straightforward or it's moving on orbit (around other object).

I think the problem is quite elementary, but I couldn't find anything that could help solve that problem using the physics on the level of basic university course (I've studied computer science, so I've got only 1 semester of physics, and basic mathematical knowledge - integrals, algebra etc.).

I know the problem can be solved numerically, but I'm interested in finding the equation describing the movement.


texts: Is our universe included inside a black hole?

texts:
This question repetitively comes to my mind but I've never found any good scientist article to argue about it, only esoteric or speculative web articles without much valuable background.

So let's suppose we're in the middle of a "black hole" ...

To me, here is why this would make sense:

Big bang

The word big bang itself may be inapproriate, indeed it is said to be an "explosion" but an "explosion" without any center.

With the idea of being inside a black-hole, it is easier to represent this as being the matter entering the black-hole. From our position, and as we are attracted by the singularity, everything seems to expand wherever we look at. And as far as we can look at, we can only see the cosmic background radiation.
Dark matter

On the contrary of matter entering the black-hole, dark matter is the matter already in front of us and we'll never be able to access it as its light (i.e. information) cannot go backward within the singularity.
Time/Gravitation

Time is a dimension like any other and as we feel x,y,z dimensions as a field of view, we fell time as an irrepressible attraction toward the singularity. Gravity may be see also as a less irrepressible dimension (depending on mass around).
Other black holes

Other black-hole we "see" may let us envision the shape of the universe not as simple torus, but higher dimensional "toric" shape with "connections" everywhere (maybe shapes like high order atomic orbitals ?).

Is there any reasonable scientific background to argue/contradict about this ?


texts: Hypothetically, if the sun stays the same size forever, when will the Earth fall into it?

texts: Hypothetically speaking (once again), if the Sun stays the same size forever (i.e. it somehow maintains a stable hydrogen supply and the helium product just disappears), how long would it take before the decay of the Earth's orbit sends it plummeting into the Sun and disintegrating?


texts: Why does the exoplanetary system TOI-178 challenges current theories of planet formation?

texts:
I am excited reading the news about ESA's latest exoplanet discovery using CHEOPS. The system TOI-178 consists of (at least?) five planets, following a 18:9:6:4:3 pattern. In the press release, the authors write:

But while the planets in the TOI-178 system orbit their star in a very orderly manner, their densities do not follow any particular pattern. One of the exoplanets, a dense, terrestrial planet like Earth is right next to a similar-sized but very fluffy planet – like a mini-Jupiter, and next to that is one very similar to Neptune.

In the few systems we know where the planets orbit in this resonant rhythm, the densities of the planets gradually decrease as we move away from the star, and it is also what we expect from theory.”

My question: What exactly does "the theory" state exactly? And why exoplanets in orbital resonance necessarily imply decreasing density of the planets if the system did not collide with any other system after its formation?


texts: Travel telescope: attaching a Lunt 80mm ed on a Dolica tripod

texts:
I'm assembling a compact and light travel telescope. I'm going for the small Lunt 80mm ed refractor telescope mounted on a light Dolica tripod.  For those with this --or similar-- assembly, I would like to ask you how did you attach the Lunt to the Dolica.

Thanks,
Marcelo


texts:
The Yarkovsky effect is responsible for changes in the rotation and orbit of some celestial bodies, most notably asteroids. It has been measured on asteroids, such as 6489 Golevka and 1999 RQ36.

What is the largest object on which the Yarkovsky effect has been observed? Scholarpedia has an excellent article and list of asteroids, but the list isn't necessarily complete, and I don't know if the effect has been detected on other (non-asteroid) bodies.


texts: I read that a few years ago some planets were discovered orbiting Alpha Centauri. Has there been any more information since then concerning the possibility of life there? This is the closest star system to Earth, but it would still take us 63,000 years to reach it.


texts: Is there any evidence that the Gas Giant planets in our solar system are experiencing orbital migration?

texts:
Planetary migration is defined by Lubow and Ida (2010) in their article Planet Migration as

  the process by which a planet’s orbital radius changes in time. The
  main agent for causing gas giant planet migration is the gravitational interaction of the young
  planet with the gaseous disk from which it forms.

Relevant, it is believed by some that the gas giant planets in our solar system experienced orbital migration.  According to the article Wandering Gas Giants and Lunar Bombardment (Taylor, 2006), as an example,

  Outward migration of Saturn might have triggered a dramatic increase in the bombardment rate on the Moon 3.9 billion years ago, an idea testable with lunar samples.

So my question is is there any evidence (not opinions) to suggest any form of migration occurring with our solar system's gas giants?


texts: Are astronomers continuously monitoring exoplanetary systems?

texts: I'm reading many of the Wikipedia pages about exoplanets and the different methods they are using to detect them.  But I wonder, it seems that the emphasis is on detecting and finding new exoplanets, but are astronomers continuously monitoring the exoplanets that have already been discovered?  For instance, if there is a collision between a detected exoplanet and a previously unknown planet, this could cause a change in some of the orbital parameters, and could be potentially detected.  If this happens, would we learn of this change, or will it have to wait until astronomers again take another look at the system?


texts: Did we discover how nebulae hold their shapes?

texts: As you know, nebulae such as the Eagle Nebula, the Cat's Eye Nebula, and the Pillars of Creation, have extraordinary shapes.  But have we discovered why that is so?  I've tried researching it myself however all that comes up are theories of a magnetic field, etc.


texts: Why do gaseous planets spin faster than telluric planets? I've seen thats because of primitive nebula but I didn't understand why? Could someone help me? I would appreciate a lot!


texts: If a Jupiter-sized sphere of a translucent liquid were to suddenly appear, what would the inner core consist of? Would the planet refract light?

texts: Assuming Jupiter is suddenly replaced, or if a giant sphere of fruit juice or other translucent mixtures/liquids were to appear bearing a similar radius to that of Jupiter, hypothetically , what would be the contents of the inner core? Would the pressure there be so high as to rip the liquids into their constituent atoms? Would light from a Sun shining on this planet be refracted through the planet's translucent body?


texts: Central temperature of a stellar model with combination of gas and degeneracy

texts:
If we have a stellar density model $\rho(r) = \rho_c(1-r/R)$, where the star is composed of ions behaving as perfect gas and electron with non-relativistic degeneracy. The central pressure is due to both gas and degeneracy pressure. My final goal is to find central temperature of this model.

Now for the linear density model, I calculated the central pressure only for gas to be $P_c = \frac{5GM^2}{4 \pi R^4}$. And central temperature for only gas is $T_c = \frac{5G \mu M_{H} M}{12KR}$

I know the Pressure for non-relativistic degeneracy $P_{nrd} = C \rho^{5/3}$. I was wondering to find central pressure for degeneracy, may I use the Lane-Emden equations for polytrops and simply find central pressure and temperature from there? Then add the two temperatures to find the maximum central temperature for a gas+degenerate star.

For Lane-Emden model, they also consider density dependence on radial distance, but they express the density function as $\rho = \rho_c \theta^n$. Is it equivalent to $\rho(r) = \rho_c(1-r/R)$ for gas model?


texts: Observations of a perigee coincident with a full Moon

texts: Hopefully this will be a quick and easy question, with a quick and easy answer, but why is it that we observe a perigee Moon coincident with a full Moon approximately every 13 months? Is this related to the Earth-Moon dynamics, perhaps the eccentricity of the lunar orbit?


texts: Is it possible to disprove geocentrism without telescopes?

texts:
The development of telescopes enabled the discovery of moons orbiting around Jupiter, and the existence of a full set of phases of Venus, as opposed to a limited set which would be predicted by geocentrism.

But is it possible to disprove, or at least make implausible, geocentrism without a telescope? Preferably without calculus or more advanced maths.

I'm curious for two reasons. One is knowing whether it was lack of technology, or humanity's attitude towards the universe, that was responsible for geocentrism. The other is that I've heard that some astronomical facts, such as the size of the earth, were calculated before the advent of telescopes, and I'd find it interesting if more facts could have been deduced even with a limited set of technology.


texts: Is there any update on the Availability of Event Horizon Telescope Images?

texts:
There has been no news on the obvious public channels from the EHT project since last (Northern) summer. Does anyone have more information on when any results from the April 2017 run might be released?

A secondary question is has the data from the April 2018 run been successfully gathered? I know they have to wait for Antarctic spring to ship the hard drives from the South pole, but that should have arrived a couple of months ago.


texts: Do some galaxies collide faster than the speed of light?

texts:
If some galaxies expand away from each other faster than the speed of light then do they collide faster than the speed of light?
Update 1:

I guess my question is what's the max speed/velocity at which galaxies can move towards each other?
How long does it take for galaxies to collide?

If you could use this example that would be awesome.
Galaxy A: diameter of 3,000 light years
Galaxy B: diameter of 300,000 light years
If Galaxy A collide with Galaxy B , what would be the velocity at the collision?
I have no idea about what the time and distance would be.


texts: I read somewhere that the galaxy is spinning too fast (in places). Therefore, there must be dark matter.  What are the equations that explain how fast the galaxy should be moving, and how are they violated?  What are the speeds and masses involved?


texts: When a neutron star accretes matter, will its mass increase?

texts:
When a nova gets matter, the outcome is that it may lose more matter because of eruptions. Only some kind of nova's masses can increase stably.

A white dwarf may become a supernova after it exceeds the Chandrasekhar limit, and we study that much. A neutron star can get mass too, why do not we talk about their end much?

How about a neutron star when it gets matter from accretion? It is necessary that its mass will increase?
When will it collapse?


texts: Why haven't asteroid belts turned into new large bodies?

texts: If gravitation (attraction of mass) is the cause of the formation of all celestial bodies then how come the numerous small bodies found in asteroid belts spread over an orbit instead of clustering together ?!


texts: Temporal path through Hertzsprung-Russell diagram?

texts: Is there graphic of typical temporal paths that stars take through the Hertzsprung-Russell diagram?


texts: Can I leave a planet without achieving escape velocity?

texts:
I know that if you exceed orbital velocity, you will never fall-back to the planet.  My question is not about orbits.  It's about brute-force propulsion to achieve altitude.  I'm using an intentionally slow velocity to help illustrate my point.

Imagine I have a rocket with very efficient fuel storage.  My rocket can store enough energy to accelerate to 100kph shortly after leaving the ground, and continue to maintain that speed (100kph) for a very long period of time.

My rocket just goes straight up.  It doesn't try to enter an orbit.  As it leaves the atmosphere, it can throttle-back because there's no air resistance.  As it continues to gain altitude in inter-planetary space, it can throttle-back even more because Earth's gravitational influence diminishes with distance.  It just maintains enough throttle to continue moving away from Earth at 100kph.

At some point, Earth's gravitational influence would be moot, as other bodies (Jupiter, Sun), would gain relative influence.  Eventually, far outside the solar system, even the Sun's influence would be insignificant.

My rocket never achieved escape velocity, but it sure did escape.

Assuming that my fuel supply could last long enough, and I wasn't concerned about travel time, could this method allow my rocket to "leave" without achieving escape velocity?


texts: Is there a relationship between stars' absolute magnitude, spectral class and relative location in a cluster?

texts:
I am interested to know whether a pattern has been observed with regard to the characteristics of a star (in particular, its absolute magnitude and spectral class) and its location relative to others in the same cluster. For example, do older, cooler stars tend to occupy the centre or edges of a cluster with greater frequency than younger, hotter stars? And do stars of a certain class and magnitude tend to appear together?

I have found no specific mention of it, but the question surely relates with theories of the formation and evolution of galaxies.


texts: Effect of Hot/Warm Jupiter atmosphere loss on other planets

texts:
Let us suppose a solar system with a Hot/Warm Jupiter HJ (with a semi-major axis somewhere from 0.5 AU to 0.0001 AU) and an Earth-Like planet EL in it (with a semi-major axis of about 1 AU). Let their orbital inclinations be a couple of degrees apart. Let the star be a G2V or so, like our Sun.

According to this and other sources, we can tell that Hot Jupiters are "bleeding" atmosphere due to their proximity to their sun. Some of it, I presume, gets pushed out with the solar wind farther out into the solar system, at least as far as the EL is.

What effect will this bled atmosphere from HJ have on EL, if any?
If there is an effect, when does it happen? On all of EL's orbit, despite the different inclinations? Only when EL crosses a transit node? Only when there's a transit (or rather, when EL passes through the transit node a certain amount of time after HJ does, to account for the velocity of the atmospheric particles through space)?
Will this bled atmosphere be (naked-eye) visible from EL? What would it look like?
Would all of this have any effect on life/civilization on the EL?


texts: Code for getting the pixel coordinates of an object with known RA DEC not working

texts:
I’m working on a project of which one of its functions is determining the XY pixel coordinates of an object given the object RA DEC coordinates and a platesolved image (this assumes that the target is near the image center).

I didn’t base this code on any algorithm, I thought it would just be basic vector manipulation. I’m aware that this basic approach doesn’t correct field flatness and stuff, I need it to be only roughly accurate.

'PS_DEC,PS_RA,PS_NORTH_ANGLE,PS_PIXEL_SCALE are retrieved from a platesolve
'Target_dec and Target_ra are the coordinates of the target
'VectorRotate(vector,angle) is a function that rotates a vector

'PS_DEC = 3.3026014754
'PS_RA = 278.7921661190
'Target_dec = 3.136138
'Target_ra = 278.65
'PS_NORTH_ANGLE = 99.89
'PS_PIXEL_SCALE = 3.15

Dim lengthTotal As Double = (90 - PS_DEC) * 3600 / PS_PIXEL_SCALE ' gets the length of the vector towards the celestial north pole in pixel

Dim InitVector As PointF
InitVector.X = 0
InitVector.Y = -CSng(lengthTotal) 'Casts the length to a vector

Dim FirstRotation As PointF = VectorRotate(InitVector, PS_NORTH_ANGLE * -1) 'rotates the vector towards the celestial north pole using north angle from the Plate Solve
Dim FlipVector As PointF
FlipVector.X = FirstRotation.X * -1
FlipVector.Y = FirstRotation.Y * -1 'flips the vector so that it points from the north pole to the image center

Dim Multiplier As Single = CSng((90 - Target_dec) / (90 - PS_DEC)) 'multiplier for applying the DEC difference
Dim FlipVectorTrim As PointF
FlipVectorTrim.X = FlipVector.X * Multiplier
FlipVectorTrim.Y = FlipVector.Y * Multiplier 'after this the vector should have the length of the Target dec

Dim Finalvector As PointF = VectorRotate(FlipVectorTrim, (target_Ra - PS_RA)) 'rotates the vector by the difference of the target ra and the ra from the plate solve
Dim Pixeloffset As Point
Pixeloffset.X = CInt(Finalvector.X - FlipVector.X)
Pixeloffset.Y = CInt(Finalvector.Y - FlipVector.Y) ' by subtracting the vectors I should get the relative offset from the image center in pixels

When I use the coordinates from the star marked green I get the yellow circle as a result, to the bottom left of the star.

Fiddling around with the code I found out that if I multiply the RA correction angle by 0.67 the target is correctly found.

Dim Finalvector As PointF = VectorRotate(FlipVectorTrim, (target_Ra - PS_RA) * 0.67)

I’ve tried this on another star where I got the same results. What I figure from this is that DEC is correctly handled, but the RA rotation is for some reason too much, by about one third.

I’ve looked at other possible error sources(placement of the circle in the image, star coordinates, the plate solve itself) and I’m confident that they are all correct, so the error has to be somewhere in this code.

I can use the fix I found, but I’d much rather know what I’m doing wrong.

Here is a link to the platesolved image.

Any help is appreciated.


texts: Serious alternate form of the Drake Equation, or graffiti?

texts:
Where I live it is very common to see jackets and T-shirts with familiar yet casually garbled or modified content (example)
I recently spotted what looked a lot like the Drake equation on the back of a motorcycle, shown in the photo.
Here is the equation from Wikipedia (more here):
$$N \ = \ R_* \ f_p \ n_e \ f_l \ f_i \ f_c \ L$$
and here is what I can make out from the photo
$$N \ = \ R_* \ f_p \ n_e \ f_l \ X \ X \ L \ B_X$$
where $X$ represents something I can't read, and note that there is a $B$ at the end that doesn't appear in the Wikipedia version.
There are also unspecified callouts on the $N, n_e, B$ and the first "$X$".
The sleeve also contains text which is only partly visible:
...CATING
...TIONS
...ALAXY

Question: Does this representation seem to reflect a serious new or alternate version of the Drake equation, or is it better or more likely characterized as "art" or graffiti?


texts:
Is our solar system affected by a body unobserved as of yet that causes our solar system to curve through space in an orbit? Is this idea outlandish or us there any evidence to support it? Consider this information:

  "In 2007 Voyager 2 unexpectedly reached the edge of the heliosphere at a distance approximately 1.5 billion km less than the distance traveled by Voyager 1, indicating the SS is bullet shaped in the direction of the interstellar magnetic field."

Another bit of information is that a binary system with a moving SS was suggested as far back in modern times as 1894 -- with predictions 40x more accurate than an earth wobble to calculate precession of equinoxes (over 100 years).

Also unknown to me was precession was observed millennia ago, for which we have some records, but today's accepted notion was formed in the 1850's -- before it was accepted that the solar system even moved. Our current theory of precession takes no account for SS movement. Zero.

Lasly local bodies do not precess at all, only distant stars and -- from what I understand -- all of them.

Is a binary star system just bunk? Can it be tested for?
Is the axial wobble theory tried tested and come up true every time or Does this theory have predictability issues that have to be tweeked constantly?
Why is it that the moons orbit around the earth, as well as the earths orbit around the sun, are increasing and the precessional cycle is speeding up? Shouldn't that have the opposite effect?


texts: Watching the Mercury transit with improvised devices

texts:
I have learned that it is not possible to watch the upcoming Mercury transit with the plain eye (using special filter glasses).

Is it possible to watch the transit with improvised devices (like a camera obscura)?


texts:
Frustratingly, I find this could be a very simplistic question and may leave me feeling a little stupid for asking it. But I have to ask this.

My lecturer keeps refering to "matter distributions" for various rotation cases, e.g., Keplerian rotation, solid body rotation, flat rotation etc etc.

I was wondering if anyone knew exactly what this term means, or the specifics for each case?


texts: Could we estimate the age of the universe based on the planar property of the Solar System?

texts:
The Big Bang scattered planets and stars everywhere in three dimensions.

But after billion years of moving and interacting with each others through gravity, planets moved on the same plane.

Given the very small but non zero friction in space, could we give a good estimate of the age of the universe?


texts: Are we sure solar cycle is not related to the orbit of Jupiter?

texts: Are we still debating the relationship between Jupiter and solar cycle? If not, what is the common or mainstream opinion about this topic? Or in other words, have we disproved the solar cycle is related to the "year" of Jupiter?


texts:
Problem: There is an satellite that orbits the Earth. Its orbit is circular and its orbital plane is perpendicular to Earth's Equatorial Plane. It orbits is such that a person who is on equator see this satellite on Zenith every 12Hours.

a. Find Satellite's Period.

b. What is distance of satellite to person when it Sets on person's horizon?

My problem with this question is:

For the first part: somewhere said period is 12hours. Somewhere else said the person on equator also moves (Earth Rotation) so 12 hours is P/2 and P= 24hours. What is the right answer?

For the second part: Which of the following figures show the position of satellite when it sets? (Figure 1 or 2?)


texts:
So I know that the Eddington luminosity is given by:

$L_{Eddington} = 4\pi GMc/\kappa$.

I want to calculate this luminosity for a plasma of purely ionized helium, as well as for an electron-positron plasma.

How do I find $\kappa$ in each of these cases? I know sometimes this is approximated as $m/\sigma_T$, but I'm not sure when to invoke this approximation, and what the respective mass would be.


texts: According to Hubble's law, the universe is expanding and this expansion is proportional to distance between the two objects and thus objects are moving away at a very fast rate,  then why is it predicted that after 4 billion years the Milky Way shall collide with Andromeda galaxy?


texts: Is gravitational lensing a good way to search for negative mass?

texts:
Is it possible to verify negative mass with gravitational lensing?  The following video proposes an idea that galaxies are surrounded by negative mass: https://youtu.be/MZtS7cBMIc4

Could this be proven or disproven by looking at gravitational lensing of distant galaxies, by looking at Hubble Deep Field images?  I would expect if negative mass surrounded a galaxy, it should cause the opposite effect of the positive mass galaxy.  If there is surrounding negative mass, there should be an “anti” lensing effect just outside the normal lensing effect.  Could someone perform this analysis and confirm or deny that idea?

Edit: In the following image, and others, I have looked to see if I could see such an effect out further from the source visually, and it is hard to tell.  There are so many galaxies in front that aren't affected by the lensing.  It might take a computer analysis of images surrounding the "ring" effect to see if there is a "radial effect" around the ring.  Most images probably don't show enough of the surrounding area to where the radial effect as predicted in the paper Izumi et al. (2013) would be apparent.  If this is present, I would think it indicates negative mass surrounding the positive mass, and would be a huge discovery confirming negative mass!  If absent, it would likely show that there is at least not a significant amount of negative mass clustered around the galaxies (wouldn't be a total disproof of negative mass).

Image from: Galaxies - Gravitational Lensing


texts: The systematic review of past observations in the hope of finding things that may have been missed

texts:
I seem to remember a TV science programme which re-examined the slides that led to the discovery of Pluto and then took a fresh look at earlier slides taken of the space which Pluto was passing through. These slides did indeed feature Pluto but were probably not part of Lowell’s search for the planet. Maybe the old data/images(if still on record) could be revisited with the advantage of later discoveries to reveal things of interest like say orphan planets?

Recently there was this case:-

https://www.extremetech.com/extreme/234037-astronomers-observed-a-nova-explosion-for-the-first-time-by-accident

Which inadvertently did this but are there any programmes/projects retrospectively doing this intentionally?’

So, it is the systematic review of past observations in the hope of finding things that may have been missed or even unknown at the time.


texts:
I'm reading about Antikythera machine and its functions.
So I read about solar cycle and moon cycle and how they used 19 solar years to compare with 235 lunar cycles.

So this is my question: They know about leap day at the time (~ 200 BC)?


texts: We cannot see the supernova remnant of the star that triggered the formation of the Sun and the Solar System, as the remnant dispersed and became mixed into the interstellar medium. So I am wondering, what is the maximum size/age of a supernova remnant/planetary nebula can reach before it can no longer be distinguished?


texts:
How large can a ball of water be without fusion starting?

Peculiar question: some explanation might be necessary. My young son is into ‘space’ and astronomy. One of his posters says that Saturn could float, if a sufficiently large ocean could be found. Obviously that wouldn’t work: Saturn’s atmosphere would peel off and join or become the atmosphere of the larger body, and then Saturn’s dense core would sink.

But could such an ocean even exist without fusion starting?


texts: Is the structure of crystalized white dwarf related to nuclear pasta?

texts:
There is news of an analysis of a large number of nearby white dwarfs revealing a "pile-up" at a certain point in their cooling which has been predicted to happen due to a phase change where nuclear material crystalizes. This is analogous to a mixture of ice and water remaining at 0C while it is in the process of freezing (or thawing).

What is this crystalline material like? Is it really a lattice of Carbon and Oxygen nuclei in some recognizable structure (cubic BCC... etc.)? Is it related in some way to nuclear pasta?

Nature: Core crystallization and pile-up in the cooling sequence of evolving white dwarfs


texts: Estimate prevalence of ʻOumuamua-style interstellar obects inside Jupiter orbit now that C/2019 Q4 (Borisov) is found?

texts:
Now we know two of them, so maybe it's not an outlier.

We have two points so we can draw a line. How many similar macroscopic objects should be zipping through space at ~30 km/sec so that we would see one of these passing inside the orbit of Jupiter once every two years? I don't really know what units this should be expressed with. Maybe it's 1 / (km^2 * year)  - the frequency of such a body coming through any random square kilometer of empty space in a year of time.

What's the "capture cross section" of intra-Jupiter orbit? I imagine that since the Sun affects trajectories of bodies coming near it, drawing them closer as they pass by, intra-Jupiter orbit will see much more bodies than a circle of same area in empty space. How large is this effect for ʻOumuamua-like bodies? I expect this is to be a unitless coefficient. Is it neligible? Is it 5x? 10x? 1000x?

Sorry if my question is not clear enough.


texts: How to calculate when Mars was in retrograde around 129 BCE?

texts:
I am trying to make an accurate illustration of the sky from when Ptolemy was observing the planets in Greece.

I am trying to find out when Mars was in retrograde during those years. I have read both SE questions and answer about how to calculate it mathematically but both of those are a little over my head.

Some of the silly astrology sites have the retrograde dates listed back the 1930s, I want to know what were the dates Mars was in retrograde around 129 BC.

https://physics.stackexchange.com/questions/249493/mathematically-calculate-if-a-planet-is-in-retrograde

https://physics.stackexchange.com/questions/288023/mathematically-calculate-if-a-planet-is-in-apparent-retrograde-motion


texts: Amateur astronomy plan for GCSE students

texts:
I'm designing an amateur astronomy observational plan for GCSE Astronomy students here in the UK. I would like some advise to the suitability of what I have selected as the content.

For the beginner level I have decided to see if they can image the
various phases of the Moon across a 28 day period.
For the intermediate level I would say they could image the Pleiades.
For the advanced level I have decided they can create a mosaic of M31
from various narrow field-of-view images. (I would suggest imaging
the LMC or SMC but we are based here in the northern hemisphere).

Would this be suitable targets over the course of a year?


texts: How do we get to know the total mass of an atmosphere?

texts:
Since atmospheres don't end abruptly but gradually get thinner the higher you go, I wonder how we can get the total mass of an atmosphere if we don't know where exactly it ends. E.g. the Earth's atmosphere's mass is defined as 5.1480 × 1018 kg. Does this value include the exosphere (which doesn't have an abrupt end either)? Or is it up to the exobase only? Or is it even the significant part only, up to the mesopause or to the Kármán line or something?
Also, if we mention the mass of a celestial body, does this value (e.g. in case of Venus 4.867 × 1024 kg) include its atmosphere's mass or not?


texts: Intuition about why gravity is inversely proportional to exactly square of distance between objects

texts: What is the intuition behind why gravity is inversely proportional to exactly square of distance between two object and not cube or not some multiplier.  Basically how Newton came up that its exactly square of distance? How it was validated it is in fact square of distance ?


texts: What is the radial dependence of the density of Jupiter or Saturn?

texts: Can anyone point me to the reference where I can find the density of Jupiter or Saturn as a function of the distance from its center?


texts: Overhead (galactic North) view of the stars in and around the Vela Constellation with distance

texts:
I am working on a project and would like to have a star map--seen from "above" (Galactic North?) that calls out the stars in the Vela constellation and shows their distance from sol / earth.

I realize that any 2D map will not show the Z-axis, but I'm okay with that (especially if there's a notation).

I want to be able to show which stars in the Vela constellation are closer to earth vs. further away.

Is there anything like this? I've looked and can't find it.


texts: Does the Earth receive any heat at all from the millions of other Stars in our Galaxy ? Is it light that is bringing the heat and perhaps it cools down on the long journey in Space getting to the Earth and that's why no significant amount of heat is getting here ?


texts: Where does the energy of light go, when it red-shifts?

texts:
When talking about the expansion of the universe, it is said that it can be proven by the red-shifting of light.(As we would need higher than lightspeed to get this redshift by the Doppler effect)

I am an amateur, so I am not sure I am correct, but here is what I think.

Redshifting increases the wavelength of the light. higher wavelength = lower frequency = less energy.

So, if my assumptions are correct, where does this energy from the light go?
If not, where did I make an incorrect assumption?


texts: What's so interesting about Coma-type galaxy clusters?

texts:
When the dynamical mass of a proto-cluster of galaxies is ~(1-2)x1014 Msolar, the proto-cluster is expected to evolve into a coma-type cluster.

In almost every paper I read about the confirmation of proto-clusters, the authors of the paper are (almost) always interested in proto-clusters (of galaxies) that will eventually evolve into a Coma-type cluster.

Why are astronomers and astrophysicists so interested in studying those type of structures (Coma-type galaxy clusters)? I mean is it interesting that a proto-cluster will eventually evolve into a Coma-type galaxy cluster? Are these structures rare in the universe?


texts: What is the largest possible size for a brown dwarf?

texts: What is the largest possible size for a brown dwarf before it has enough mass, capable of sustained fusion, thus becoming a star?


texts:
Do any numbers in between 80 and 85 (or thereabouts) hold any relatively important or relatively obvious meaning in ancient astronomy ?

A few clarifications:

By ancient I mean related to human antiquity. (Thus, for instance, although in modern times there are indeed 88 known constellations, almost half of them were unfortunately unknown to the ancients).
The meaning in question could refer, for instance, to the number of time periods in a specific time cycle, or to the number of stars in a certain constellation, etc.
By relatively important or relatively obvious I mean something as self-evident and meaningful  to an ancient sage as the fact that there are roughly 360 days a year, or that the number of constellations in the northern and southern hemispheres are 21 and 15, respectively (as known to the ancient Greeks, for instance).

Some background information:

About a century ago, an archaeological site, located in a clearing in the woods, and dating back to the first two centuries BC, was discovered at 45.62°N and 23.31°E, at an altitude of roughly 1,000 meters.

The structure, oriented on a NNW-SSE axis, consists of four concentric circles, the second and fourth of which (counted from the exterior towards the interior) have a clear calendrical and astronomical interpretation, pointing to a semester of 180 days, divided into exactly six months of thirty days each, and to a number of 21 + 13 constellations in the boreal and austral hemispheres, comparable to the figure given by the astronomer Claudius Ptolemy in his famous Almagest. I was wondering whether the third circle, consisting of a number of no less than 82, and no more than 84 pillars, might not also have a similar meaning. Now, don't get me wrong, interpretations abound, but most of them tend to be either slightly forced, or are outright pseudo-science.

As an interesting aside, there were, initially, only 68 pillars still standing, which just so happened to be double the number of those which constitute the inner horseshoe (as it is called), making many archaeologists speculate that its builders were aware of the fact that after 68 semesters of 180 days, corresponding to a number of 21 + 13 = 34 years of 360 days, the calendrical error would amount to almost an entire semester. All nice and tidy, but this proposed solution suffered a devastating blow when further excavations, performed by the son of the man who initially discovered the site (both were historians by profession) revealed that the number of pillars comprising the third circle was much higher than previously thought. Furthermore, a certain scientist has already started speculating that the number of elements should be about 84 long before the excavation in question even happened in the first place! (He based his ideas on the fact that if the second circle represents the solar year, and the fourth one basically corrects it, then there should also be a refinement to the nice-but-inaccurate 30 day month as well). However, even this little gem of a theory has a small and insignificant scratch: One of the main reasons why 84 year lunar cycles were even considered in the first place was because its value is a multiple of 28, the latter representing the number of years in a perpetual calendar synchronizing the seven day week to the solar cycle... Just one minor glitch, though: The civilization that built the structure had months of thirty days, divided into five six-day weeks, as is evidenced by the clear and uniform distribution of the pillars forming the second circle. (Certainly, it is not completely impossible for them to have borrowed such a time-correcting mechanism from other neighboring cultures, but it's not highly likely either). So, herein lies the dilemma...


texts: Seeing a galaxy (quasar) greater than 46.6 billion light years away

texts: Assuming the Big Bang was 13.8 Billion Years ago: Is it possible to observe a Galaxy's redshift showing distances slightly greater than that, like 48 Billion Light Years away? I understand that in a static universe, light traveling in a straight line would only be visible at less than 46.6 Bly. But, can Hubble's constant distort this number? Also, do we assume some error due to the light taking a non-linear path because of lensing? If so, is it possible to have an error of several hundred million years?


texts: Is it possible to use a laser to propel a spaceship?

texts:
Reference: http://adsabs.harvard.edu/full/1968BAN....19..421H
It would be necessary to aim a laser to the target star. How would the density of the laser compare with the interstellar radiation?


texts:
I am trying to find a started telescope for my high school sister and my goals are to have awesome pictures and to let her explore her interest in the stars!

They live in a clear night sky area so Im looking for the best bang for my buck.

Right now I have picked out 3 telescopes, 2 reflectors and 1 Refractor. What qualities should one look for?

How do I compare telescopes to judge which will work best with a camera and is easy to learn?

What matters most for these conditions? Aperture, Focal Length, or the Focal Ratio?

What type of telescope would be best in terms of my goals?


texts: A Sky Map of Gravity - what would it look like?

texts:
PREAMBLE

Sky Maps exist which show the distribution and intensity of electromagnetic radiation received on Earth at various wavelengths.  An obvious form is a map of the stars (Star Chart).

Maps have also been made for the distribution/intensity of Cosmic Microwave Background Radiation and "to visualize the X-ray Universe".

I find it interesting to consider the appearance of a Sky Map which showed the variation in intensity of the Gravitational Attraction Force (as currently experienced on Earth) attributable to masses lying in different directions (looking radially outwards from the Earth).

Essentially (if we start with a Newtonian Model) this would be a map which indicated the magnitude of the sum of "mass/distance_squared" for all the masses falling inside each particular pixel of the map.  This then raises the questions of cosmological nature e.g. "how far do gravitational influences extend away from the Earth", along the lines of Olbers Paradox and "how was matter distributed through the Universe through time" - see The Cosmological Principle.

QUESTION

To bring this into the form of a question that can be answered succinctly, my question is: "What would a SkyMap of Radial Gravitational Force, looking outwards from Earth, look like (excluding that due to masses in the Solar System and Milky Way galaxy)."

APPENDIX

Calculation of Average Background Gravitational Force from Visible Universe

(Assuming, for simplicity, a static, spherical, universe of uniformly-distributed ordinary matter with Newtonian gravity and a test mass at the centre of the universe).

$\rho$ Average density of visible matter  $=3*10^{-28} Kg/m^{3}$

$R$ Radius of visible universe   $=1.7*10^{26} m$

Note:- values of $\rho$ and $R$ are obtained from here.

$G$ Universal Gravitational Constant  $=6.673*10^{-11} Nm^{2}Kg^{-2}$

$f$ Fraction of sky represented by $3.6 * 3.6$ degree rectangular pixel $=1/(50*100)$ $= 0.0002$.

The formula for Force per unit mass $F_m$ is obtained by integrating (over the interval $0,R$) the incremental force per unit mass $F_i/m = G.M_i/R_i^2)$.

Here $M_i$ is the incremental mass contained within the incremental volume $V_i$ of the spherical shell of radius $R_i=R_{i-1}+\text{d}R$ and given by $M_i = \rho.V_i \approx \rho.4\pi.R_i^2.\text{d}R$.

Thus the total force/unit mass is given by:-

$$ F_m = G\int_0^R \frac{\rho.4\pi.R_i^2}{R_i^2}\text{d}R  = 4\pi G \rho R $$.

And so the force per unit target mass per pixel is given by:-

$$F_{m,f} =4\pi G\rho R f  = 0.86*10^{-14} NKg^{-1}.$$


texts: What is the angle of the Sun on the eastern horizon at 35° latitude if it is the winter solstice?


texts: What is Earth believed to have looked like before the collision with Theia?

texts:
Let's assume the moon was formed because Earth collided into Theia. (There are numerous other theories, but this one is the most widely accepted.)

In that case, are there theories that address what the Earth surface looked like? E.g. would the Earth have had bodies of water at the time?

I've read some websites and a book!, and some say it did, some say it did not.


texts:
In a sense, humanity has long been capable of transmitting interstellar messages (METI (messages to extraterrestrial civilizations) - attempts to transmit interstellar messages from humanity to probable intelligent beings outside the solar system.)
The first strong generalization sent into space was probably ... Hitler's speech.
This short television program, literally a few minutes, was broadcast in 1936 from Berlin with the opening of the Olympic Games.  Although it was only received in Germany, it was the first, albeit weak, transmission from Earth.  Unlike conventional radio broadcasting in the 1930s, TV signals pierced the ionosphere and went into space.
After that, the broadcast of the coronation of George VI took place in England and something else of the same kind.  Truly television began only in the late 40s.  And all the signals of those years are carried away from the Earth at the speed of light.
However, all of these signals are extremely weak.  After passing only a couple of light years, they will fade out and it will be almost impossible to catch them, much less decipher.
Why?
The main problem with sending interstellar messages is that as the distance traveled increases, their power gradually decreases due to gradual scattering (diffraction).  Imagine that you have thrown a stone into the calm surface of a lake: from the original stone the circles began to diverge in all directions, but the further they diverge, the less noticeable they become.  The same thing happens with radio waves: if you calculate approximately, then twice the distance from the communication source will reduce the power of the radio waves by four times.  As you can see, detecting such radio waves at a distance of several hundred light years from Earth will be a difficult task for space civilizations.
And here we come to the heart of the question:
What is the nature of the interstellar message to be accepted by a civilization comparable to humanity at the end of the nineteenth century (19)?
After all, as mentioned above, radio waves are not very effective for interstellar communication.
In addition, if Arecibo's message had come to us in 1913, we would not even have been able to receive it.


texts: How does the gravitation of Jupiter or other big planets affect Kepler's third law?

texts:
Does anyone know a good reference for this?
I once read how Jupiter's gravitation can be treated as a perturbation. I think they expanded Jupiter's gravitation as an infinite sum of one of the special functions (such as Bessel function, Legendre function, Hermite polynomial, I can't remember).
I am not interested in how the motion of a planet at each time looks like, but just the overall effects on parameters such as period, semi-major axis, and eccentricity.


texts: Orphaned star systems and intergalactic travel (in fictional context)

texts:
Context:
I'm looking for some authority on a particular idea that I brought up in regards to a new update brought out for a space travel sim game, Elite Dangerous

The vessels in that game can travel between star systems, requiring fuel- they can only jump between star systems, and have a limit on how many light years they can travel in one jump.

The latest update added a vessel that can jump up to 500 light years.

Vessels can't travel continuously to a location, it has to be point to point, i.e. teleportation (sort of)

The question:

Given the context above, can it be estimated that there are enough high orbiting, or orphaned star systems between the edge of the milky way, and the edge of the Canis Major dwarf galaxy for one of these vessels to traverse a 'corridor' of 500ly (or closer) intervals of star systems between the two galaxies?


texts: Tests for code that computes two-point correlation function of galaxies

texts:
I'm currently writing a code to compute the two-point correlation function of a set of galaxies. As I work with a loooot of galaxies, it was suggested to me not to do it in real space, but to compute the power spectrum in Fourier space and get the correlation from the power spectrum, as is explained e.g. in appendix B in this paper (arXiv:1507.01948).

What I need are some very simple test cases with known results to test my code at each step in order to ensure that I really get what I want. Can anybody point me to any such simple tests? Or at least to a already existing code (preferably in Python or Fortran) that does exactly this, so I can cross-compare the results?


texts: Why Do Planets Revolve Faster When they Are Closer to Their Parent Star?

texts: According to Kepler's second law: A planet sweeps out equal areas in equal times (A simple definition). This means that if the orbit is somewhat eccentric, the planet will move faster when on the closest approach to it's parent star, and slowest when at aphelion. So why does this happen, is the curvature of space-time greater closer to the star?


texts:
I'm very new at Astronomy, and my knowledge is sparse. I've tried to be conscientious about my Wikipedia research but there's going to be a lot of things I don't know. Thanks for your patience.

BACKGROUND

I had read that hot Jupiters can cause superflares due to magnetic recombination. But checking Wikipedia I came across the following:

  Not all planetary transits can be detected by Kepler, since the planetary > orbit may be out of the line of sight to Earth. However, the hot Jupiters > orbit so close to the primary that the chance of a transit is about 10%. > If superflares were caused by close planets the 279 flare stars
  discovered should have about 28 transiting companions; none of them
  actually showed evidence of transits, effectively excluding this
  explanation.

- Wikipedia

QUESTION

Given this, and among modern astronomers in general, is the theory that hot Jupiters can cause superflares on the outs? Or is the article just saying that hot Jupiters can't explain these particular stars, while the model remains valid elsewhere? Do we have any solid evidence of a gas giant causing solar flares, super or otherwise?


texts: Identifying common galaxy spectral lines

texts: How does one identify the common galaxy absorption lines (e.g. Na, Mg, K, etc.) and emission lines (H-alpha, O III, S II, etc.) by just looking at a galaxy spectrum (like the one below)? I need to know how to do this because I want to calculate the redshifts of galaxies using the emitted wavelengths from the SDSS table.


texts: What would the effects be on Earth if Jupiter was turned into a star?

texts:
In Clarke's book 2010, the monolith and its brethren turned Jupiter into the small star nicknamed Lucifer.  Ignoring the reality that we won't have any magical monoliths appearing in our future, what would the effects be on Earth if Jupiter was turned into a star?

At it's closest and furthest:

How bright would the "back-side" of the earth be with light from Lucifer?

How much heat would the small star generate on earth?

How many days or months would we actually have night when we circled away behind the sun?

How much brighter would the sun-side of earth be when Lucifer and the sun both shine on the same side of the planet?


texts: Frequency analysis on Semiperiodic object(s) using Lomb-Scargle

texts:
So I already did a frequency analysis of the SRv-type's light curve  using Period04. I already have the 'periodicities' of the object/star of choice which is quite hard since the latter/other periods are tucked away by yearly aliases (thank goodness that's a rough week).
The problem, however, is that the mentioned-software doesn't allow the user to acquire the Power Spectrum but only the Fourier data (as of the moment) which is important for visualizing the non-coherent signals. May I kindly ask if it's possible to deduce/extract the power spectrum from the fourier data using Lomb-Scargle periodogram? And if there's an existing python tool/code to it?
The current code, which is below bog standard I'm afraid, just visualizes the Fourier spectrum;
import pandas as pd
import matplotlib.pyplot as plt
with pd.option_context('display.float_format', '{:0.20f}'.format):
    data = pd.read_csv('FLSP.csv')
    print(data) #shows Frequencies/Amplitudes

x = data['Frequency']
y = data['Amplitude']

plt.xlabel('Frequency')
plt.ylabel('Amplitude')

plt.plot(x, y)

Which should give you something (as useless) like this;

It's the Long Secondary Period (LSP) of the variable star at ~2350 days. Attach here is the fourier data if you want to check out.
Help at this point is sincerely appreciated. Thnx a lot and clear skies.
Note: I tried using Astropy's and Scipy's Lomb-Scargle, and their implementations require the observations; light curve, so I'm stuck on 'looking' at the fourier spectrum...suggesting to me that's its back to square one (hoping not lol).


texts:
So I need to estimate the mass of the andromeda galaxy using:
$$ M = \frac{v^2r}{G}$$
where $v$ is the rotational velocity, $r$ the galaxy's radius and $G$ Netwon's gravitational constant. I'm told the following:

Distance (m) = 2.403×$10^{22}$
Radius (arcmin) = 12250.40
Velocity (km/s) = 300

I went so far as to convert the radius:
$$ \frac{12250.4}{60*57.3} = 3.563\ rad$$
then, calculated the radius:
$$0.5*3.563*2.403\times10^{22} = 4.2757\times10^{22}$$
Then subbed into original formula to get:
$$\frac{ 4.2757\times10^{22} \times 300^2}{G} = 1.7595\times10^{36} kg$$
It should be $2\times10^{42}kg$. where have I gone wrong?


texts: Do we make predictions in our time, or local time?

texts:
I was scrolling idly through the Wikipedia article on Orion when I read:

  Orion will still be recognizable long after most of the other constellations—composed of relatively nearby stars—have distorted into new configurations, with the exception of a few of its stars eventually exploding as supernovae, for example Betelgeuse, which is predicted to explode sometime in the next million years.

Given that Betelgeuse is only 640 light-years away from Earth, the question of whether we're talking about Betelgeuse going supernova in the next million years, or about news of the supernova reaching us in the next million years, is irrelevant, since 640 years is hardly noticeable when you're talking about ten thousand centuries.

But what about a star further away? Say, something in the Andromeda Galaxy, 2.5 million light-years from us? If I read an article stating that a star in the Andromeda Galaxy was going nova in a million years, would that mean:

a) That we think the star will go nova one million years from now, and its light will reach us in 3.5 million years; or
b) That we believe the star went nova 1.5 million years ago, and its light will reach us in one million years

In other words, are we making estimates in our time, or in celestial-body-local time?


texts: How can the equation of state for cosmic strings and domain walls be derived?

texts:
In this article which nicely explains why it is really the quantity $\rho + 3p$ which is relevant to determine if the expansion of the universe is accelerating or decelerating by making use of the for this question relevant second Friedmann equation

$$
\frac{\ddot{a}}{a} = -\frac{4\pi G}{3}(\rho + 3p)
$$

it is mentioned that for cosmic strings

$$
p = -\frac{\rho}{3}
$$

which has the effect that they dont contribute to the "non-inertial" expansion of the universe, and for cosmic domain walls we have

$$
p = -\frac{2 \rho}{3}
$$

which leads to an accelerated expansion of the universe.

Whereas I understand the derivations of such equations of state for radiation, "ordinary" matter, and a constant source of dark energy, I have not yet seen analog calculations for cosmic strings and domain walls.

So how can the equation of states for topological defects such as cosmic strings and cosmic domain walls be derived?


texts: What is the centre of rotation of Pluto?

texts: I know that Pluto and Charon have been found to circle round each other, hence the reason Pluto is no longer a planet I believe, which would mean that the centre of rotation is an arbitrary (!) point somewhere between the two of them. Where is it please? Can it be calculated?


texts: Total solar eclipse, supermoon, and spring equinox all happening at the same time: anything special about this?

texts:
Today (March 20, 2015) is seeing a rare combination of the spring equinox, a total solar eclipse, and a supermoon.  I am wondering if there is anything special astronomically about all three of these happening at the same time, like is the equinox a particularly more or less likely time for solar eclipses to happen (my guess is that it has no impact eclipses).

The supermoon/total solar eclipse combination doesn't seem surprising to me, since if the opposite were to happen (moon far away and solar eclipse) we would end up with an annular eclipse instead of a total eclipse.


texts: Doesn't gravity attract objects in space until they collide?

texts:
If the formula to calculate the force of gravity between two objects is:

$$F = GM_1M_2/r^2,$$

why do planets stay in orbit? Or is there another formula at work?


texts: Astrophotography: Is there a rule to the color mapping?

texts: As I understand it most astrophotography is colored using filters and multiple exposures. I would assume that blue filters would be used for higher frequency emissions and red filters for lower frequency emissions, as it at least keeps the "order" of information intact. But besides that, is there any rule or hints to go by when looking at colored astrophotography and deducing the depicted wavelengths? Because a fairly common problem would be, I assume, when something is only visible in either infrared or ultraviolet. How would I differentiate that? Do I just have to know what emission bands certain phenomena are visible in?


texts:
For every year, the moon is orbiting further away from earth.

What distance has the moon been from earth at the closest?


texts: How are people converting intensities in Janskys to Kelvin?

texts:
I'm reading some ALMA proposals and I am often seeing a conversion from Jy to Kelvin when, for example, people quote noise levels or source flux.

For example on their sensitivity calculator
(https://almascience.nrao.edu/proposing/sensitivity-calculator) 1 mJy is equivalent to around 1 K when the angular resolution is 1". I can tell it somehow depends on the resolution because it won't give me a conversion unless I enter a resolution.

What's happening under the hood here? And why does their documentation treat sensitivities entered in Kelvin differently from when they're entered in Jy? Is this an interferometry thing?

Thanks


texts:
This question pertains to this article which talks about why the BICEP2 measurements of B-mode polarization in Cosmic microwave background radiation turned out to be noise from galactic stardust. They go on to add that the Plank data of the noise does not lend to getting a good B-mode estimate from the BICEP2 data.

  However, the results of the joint assessment would suggest that
  whatever signal BICEP2 detected, it cannot be separated at any
  significant level from the spoiling effects. In other words, the
  original observations are equally compatible with there being no
  primordial gravitational waves. "This joint work has shown that the
  detection of primordial B-modes is no longer robust once the emission
  from galactic dust is removed," Jean-Loup Puget, principal
  investigator of Panck's HFI instrument, said in the Esa statement.
  "So, unfortunately, we have not been able to confirm that the signal
  is an imprint of cosmic inflation."

Can someone explain why(from a signal processing perspective) exactly the detection of primordial B-modes is not robust even after the emission from galactic dust is removed? And what are the proposed workarounds to tackle this problem?


texts:
Every night I see this constellation from my window but I can't identify it. What is this constellation called? Also, it would be helpful if you could clarify on the other stars as well.
Actual photo:

Pattern:


texts: Converting Earth Moon Barycenter coordinate to Geocentric coordinate

texts:
I have Earth Moon Barycenter coordinate (J2000) generated from VSOP2013 in Astronomical Units,

JD=2415020.5
X=-0.1968857640    Y=0.9633224602     Z=0.0002147057    AU
X'=-0.0171376156   Y'=-0.0035078892   Z'=-0.0000011481  AU/day

How to convert it to Geocentric?


texts: Does light from the sun reach the surface of Venus

texts: I am aware we have images from the surface of Venus from the Venera missions but I am not sure if those images are taken using the visible spectrum the human eye can see. This is why I was wondering if light reaches the surface of Venus with how dense the atmosphere is or would it be pitch black?


texts: Are the radial spokes in Saturn's rings reliably visible via ground-based telescopes

texts:
In the mid 1970's, Franklin and O'Meara saw persistent "radial spoke-like features" in the rings of Saturn, that should not have existed due to the differential rotation of the rings.  A publication on this observation was rejected by a journal apparently on the grounds that the phenomenon was considered to be illusory (c.f Sciparelli/Lowell's Martian canals?).

  From "Seeing in the Dark: How
  Amateur Astronomers Are Discovering the Wonder" By Timothy Ferris.

My question is, how reliably were these features visible from the ground-based telescopes of the day?  Could sufficiently strong evidence for the existence been obtained before images from space probes?  Was the rejection of the paper reasonable in the historical context in which the paper was submitted?


texts: What would the night sky look like if Earth orbited an intergalactic star?

texts:
If the Earth and its host star were located exactly in-between the Milky Way and Andromeda would the night sky be completely void of light?

Would stars be visible to the unaided eye?

So there could be a civilization that exists in which the night is completely void of light? …that would suck


texts: How was the hypothetical ninth planet kicked so far out of the Solar System?

texts:
I was reading this article on science news and ran into the following statement:

  Such a remote super-Earth probably originated closer to the sun only to be kicked out by the other giant planets during the solar system’s formative years, Batygin and Brown suggest.

I was wondering, how was this planet kicked so far out of the Solar System?
Why only one planet?


texts: Right Ascension, Declination from pixel coordinates

texts:
I have an Excel spreadsheet that will take certain keywords from a FITS image header. Image centre RA, Dec, rotation, x centre, y centre, x scale, y scale.
I enter the pixel coordinates of an object and the spreadsheet returns the RA and DEC coordinates.
Close to the centre of the image the results are good, but an error increases towards the outer parts of the frame.
I believe there are Python programs for doing this but my experience with Python,  C++ is zero.

Does anyone know how accurate coordinates can be obtained, using arithmetic suitable for excel and Visual Basic?


texts:
I need to calculate the exact moon phase angle for each our of a day. I have my position in lat and long and a unix timestamp. At the end i would like to be able to caluculate the moon brightness with this formula: https://patents.google.com/patent/DE10113295A1

const moonPhaseAngle = Math.cos(( 2 * ( ( phase * 100 ) / 100 ) -1));

const moonBrightness = 10 * Math.sin( altitude ) * ( .5 + ( .5 * Math.cos( moonPhaseAngle ) ) );

This is my actual progress through web search.
Thank you for helping me!


texts: Lagrange points and the radius of the Hill sphere

texts:
(Disclaimer: I know the "Hill sphere" is just an approximation of something which isn't genuinely spherical.)

In a two-body system, the approximate formula for the Hill sphere radius of the smaller body is

$$r_{\mathrm{H}} \approx a (1-e) \sqrt[3]{\frac{m}{3 M}}$$

where $a$ is the semi-major axis of the small body's orbit around the larger, $e$ denotes that orbit's eccentricity, $r_H$ is of course the radius of the Hill sphere, $m$ is the mass of the smaller body and $M$ is the mass of the larger one.

If and when the eccentricity is negligible, this is approximated further to

$$r_{\mathrm{H}} \approx a \sqrt[3]{\frac{m}{3M}}$$

This formula is often used to approximate the distance between the smaller body and the L1 and L2 Lagrange points, although these distances are not in fact identical (L2 being further distant than L1.)

The distance $r_1$ between the smaller body and L1 is obtained by solving this equation (which appears also to assume negligible eccentricity):

$$\frac{M}{\left(a-r_{1}\right)^2}=\frac{m}{r_{1}^{2}}+\frac{M}{a^2}-\frac{r_{1}\left(M+m\right)}{a^3}$$

Similarly, the distance $r_2$ between the smaller body and L2 is obtained by solving:

$$\frac{M}{\left(a+r_{2}\right)^2}+\frac{m}{r_{2}^{2}}=\frac{M}{a^2}+\frac{r_{2}\left(M+m\right)}{a^3}$$

As noted above, $r_H$ as obtained using the approximate formula approximates both $r_1$ and $r_2$.

Various online sources use language such as "The Hill sphere lies between the L1 and L2 Lagrangian points" or "the Hill sphere extends somewhere between the L1 and L2 Lagrangian points". I find this language unclear, and can't tell which of the following these sources are saying:

$r_H < min(r_1, r_2)$

$r_H \leq min(r_1, r_2)$

$r_H < max(r_1, r_2)$

$r_H \leq max(r_1, r_2)$

$r_1 < r_H < r_2$

$r_1 < r_H \leq r_2$

$r_1 \leq r_H \leq r_2$

$r_1 \leq r_H < r_2$

or something else.

As I write this, I'm not sure how trivial a task it would be to work through the approximations for the L1 and L2 points to determine if the Hill sphere radius formula overestimates or underestimates each, so I apologise if this is something other users of Astronomy SE would find trivial.


texts:
Sorry for the absolute begginer question here, but is our sun a part of some globular cluster?
It is something related to Virgo supercluster?